The present invention relates to a display apparatus. More particularly, the present invention relates to a display apparatus including a RGB color combiner and a 1D light valve relay including a Schlieren filter.
Light modulators are used to modulate one or more wavelengths of light. Light modulators can have applications in display, print and electrical device technologies. Examples of light modulators, and in particular grating light valve type devices, which utilize suspended micro-ribbon structures to modulate light are disclosed in the U.S. Pat. Nos. 5,311,360, 5,841,579 and 5,808,797, all issued to Bloom et al., the contents of which are hereby incorporated by reference.
Briefly, a grating light valve type device described in the above referenced patents includes a series of elongated, reflective ribbons arranged adjacently and in parallel. When the ribbons lie in an un-deflected, or flat, state, an incident beam of light reflects off the grating light valve type device as a mirror. If alternating ribbons are pulled down, or deflected, then the incident light diffracts. In operation, a through-state is considered to be when the alternating ribbons are deflected by a predetermined distance, thereby obtaining maximum diffraction of the incident light, and the diffracted first order light may be collected. Inefficiencies arise since the first order light is not the only diffracted light in the deflected state. Higher orders of light are also produced including second order, third order, etc. These higher orders are not collected and are therefore wasted. This reduces efficiency.
Problems arise in association with the collection process of the first order light. When the incident light is diffracted in the through-state, different wavelengths diffract at different angles. Larger wavelengths have larger diffraction angles. As such, any wavelength combiner used for collecting the first order light must be sufficiently large to account for the varying wavelength diffraction angles. A wavelength combiner is also called a wavelength multiplexer, examples of which include a dichroic filter, a diffraction grating, and an array waveguide. Unfortunately, the larger the combiner, the less efficient is the collection process and the lower the contrast ratio provided.
Design of the optical system must not only account for collecting of the plus and minus first order light, but also must isolate the first order light from the higher order light and any reflected light. Since the different wavelengths diffract at different angles, the optical system must ensure sufficient discrimination of zero and first order diffraction of all wavelengths encountered in the system. Considering the isolation and collection constraints of such a system, the optical design considerations using a conventional grating light valve type device are substantial.
What is needed is an optical system utilizing light modulators that efficiently combines multiple wavelengths of light and also isolates, or filters, specified states of the combined light.
An embodiment of the present invention includes an optical system. The optical system includes a plurality of light modulators, one or more combining filters, and an optical relay system including a filter. Each light modulator modulates a corresponding incident light beam. The one or more combining filters superimpose the modulated light beams from each of the plurality of light modulators. The optical relay system filters the superimposed light and relays the filtered light to an image plane.
Each light modulator is preferably a grating light valve type device. The optical relay system is preferably a modified Offner relay type device including a primary mirror and a secondary mirror. The primary mirror preferably receives the superimposed light from the one or more combining filters off-axis. The filter within the modified Offner relay type device is preferably located at a transform plane of the modified Offner relay type device. The secondary mirror preferably includes the filter. The filter within the optical relay system is preferably a Schlieren type filter. The combining filters can be dichroic filters.
Each light modulator preferably modulates the light by reflecting a portion of the incident light beam as zero order light and by diffracting another portion of the incident light beam as first order light. The zero order light can be relayed to the image plane or the first order light can be relayed to the image plane. The optical system can also include a color correction lens coupled between one or more of the plurality of light modulators and the combining filters.